Brake test stands are known e.g. from DE patent 196 35 194. Said known brake test stand comprises two rollers arranged parallel to each other, on which a vehicle wheel is positioned. One of the rollers is driven by a respective drive while the vehicle wheel, positioned thereon, is braked. The function of the vehicle brake is estimated on the basis of the braking force acting on the roller.
From DE laid open document 10 2009 016 498, a device and a method for measuring the tread profile of a tire which is mounted on a vehicle wheel is known. The tire to be tested stands on a surface wherein the tire is deformed due to the weight of the vehicle. A light emitter is arranged in front of the tire and emits light in an acute angle to the tire. A sensor which may be a two-dimensional camera, detects the reflected light and creates a tread profile. Based on said profile, tire conditions may be estimated.
From PCT patent application WO 98/34090, a method and a device for measuring the tread depth of a tire mounted on a vehicle is known. The vehicle wheel is positioned on two rotatable rollers. A linear light beam is directed to the surface of the tire from a light source positioned below the rollers. The light source is aligned between the rollers and approximately vertically below the wheel positioned on said rollers. The reflected light beam is sensed by an image defining sensor so as to obtain data related to the tread depth of the tire. During the measurement operation, the tire is rotated to obtain data from various places on the tire or of the complete running surface of the tire.
In EP patent application 0 816 799, diagnostic information regarding the tire tread, balance conditions and the wheel alignment are captured by a contactless measurement of the tire tread. A laser beam or stripe, respectively, is directed to the running surface and the side walls of the tire during a complete revolution of the vehicle wheel. The vehicle wheel may be mounted on a wheel balancer on a known brake test stand including rollers on which said wheel is positioned. A tire tread image is created and, based on said tire tread image, characteristics of the tire conditions are determined, such as the tread depth or wheel alignment.
In the known wheel diagnostic systems, brake test stands and wheel balancers, each wheel or tire is tested separate from each other wheel or tire of the same vehicle. Moreover, on a brake test stand, including a single roller or a pair of rollers, on which both wheels mounted on the same axis, are positioned, the brake force measurement of each of said two wheels is influenced by the respective other wheel.
Thus, it is an object of the present invention to provide a brake test stand and a method for testing vehicle brakes, with which the diagnostic measurement of vehicle wheels, in particular, the accuracy of the measurement results is improved.